Optical recording disks of the write-once, rewritable and other types have been of great interest as high capacity information bearing media. Among the write-once optical recording disks, those having a recording layer predominantly comprising a dye have the advantage of low cost manufacture because the recording layer can be formed by coating.
There were commonly used disks of the air-sandwich structure having an air space on a dye layer. Recently disks of the close contact type having a reflective layer in close contact with a dye layer were proposed because they could be reproduced in accordance with the compact disk (CD) standard. See Nikkei Electronics, Jan. 23, 1989, No. 465, page 107; the Functional Dye Department of the Kinki Chemical Society, Mar. 3, 1989, Osaka Science & Technology Center; and Proceedings SPIE--The International Society for Optical Engineering, Vol. 1078, pages 80-87, "Optical Data Storage Topical Meeting", 17-19, January 1989, Los Angels. The optical recording disks of the close contact type are fabricated by forming a dye layer, a reflective layer and a protective layer on a transparent substrate in the described order so that the reflective layer is in close contact with the dye layer, meeting the disk total thickness of 1.2 mm required by the CD standard.
In order that optical recording disks having a dye base recording layer be reproduced by means of a CD player, a gold (Au) reflective layer is used in one proposal because the aluminum reflective layer used in conventional CDs has insufficient reflectivity. Although gold has high reflectivity and corrosion resistance, it is expensive. It is thus contemplated to use less expensive metals having reflectivity as high as gold, for example, copper and copper alloys.
Disks having reflective layers of copper and copper alloys, however, are less reliable because copper and copper alloys are reactive with the dye, causing deterioration of the dye and a lowering of signal outputs. Especially, copper is chemically reactive with cyanine dyes which are often used in the recording layer. Cyanine dyes are typically used in the form of an ionically bonded combination or a mixture with a metal complex quencher in view of light fastness. Copper is also reactive with the metal complex quencher, raising a further problem.